Plug fuse



July 14, 1942. F. G, VON HOORN 2,289,944

PLUG FUS E Filed Dec. 3, 1940 Irwvevtof: Fred @1A/Oh Hoorn,

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Patented July 14, 1942 UNITED STATES PATENT OFFICE General Electric ComNew York pany, a corporation of Application December 3, 1940, Serial No.368,333

(Cl. 20o- 130) 3 Claims.

My invention relates to electric fuses, and more particularly to plugfuses of the type which are adapted for use in residence wiring systems.

An object of my invention is to provide a new and improved fuse of thetype described, in which the number and arrangement of the parts havebeen greatly reduced and simplified resulting in a fuse which may bemanufactured at low cost.

Another object of my invention is the provision of an improvedindicating arrangement within the fuse structure to designate the ratingof the fuse.

In the accompanying drawing Fig. l is a View of a plug fuse constructedin accordance with my invention; Fig. 2 is a plan view of the top of thefuse; Fig. 3 is a cross-sectional view through the fuse body; and Fig. 4is a perspective View of a portion of the fuse structure showing theindicating arrangement.

Referring to the drawing, my fuse is similar to a standard plug fusecapable of being inserted in any standard fuse receptacle such asemployed in residence wiring systems. The fuse includes a body ofinsulating material IU, a fusible element or link I I, a screw-threadedshell I2 and a center contact I3. The latter two elements form a Contactmeans for making an electrical connection between the fuse and thecontacts of the fuse receptacle.

The body I of the fuse is formed of insulating material and, in theinstant case, is formed of a transparent insulating material. Examplesof such a material are glass, or a molded plastic material. I prefer tomake the body of glass. At one end the fuse body is provided withknurled sections I4 for gripping the fuse to thread it into a fusereceptacle. At the other end the fuse body is formed with a recess I5which extends inwardly to a point adjacent the top of the body. Thebottom wall I6 of the recess forms, in eect, a window through which theinterior of the fuse body may be Viewed. The window is formed with anarcuate surface I'I on the top of the fuse body which acts as a lens tomagnify the size of the fuse elements positioned within the body.

At its open end the recess I5 is closed by means including a disk I8resting on a plate I9. These elements are held in position by ascrew-threaded shell 20. Both the disk I8 and the plate I9 are formed ofinsulating material, for example, a relatively inexpensive insulatingmaterial such as sheet liber. The plate I9 carries the aforementionedcenter contact I3. In mounting the contact on the plate the contact isrst inserted through an opening 2l and the end of the contact is thenpeened over, as shown at 22, to secure it rigidly in position on theplate. The threaded screw shell 20 is secured to the body I0 byfrictional engagement with serrations 23 formed on the outside perimeterof the body III conforming substantially to the configuration of thethreads on the screw shell. At one end the threaded screw shell isprovided with an inwardly turned ange 24 for engaging the plate I9 sothat as the disk I8 and the plate I9 are positioned to close the recessI5 the threaded screw shell holds these elements in position whenmounted on the fuse body. The center contact I3 extends through anopening 25 formed by the rim o f ange 24 so that this contact iseiectively insulated b y the plate I9 from the iiange of the screwshell.

As shown more particularly by Fig. 4, the disk I8 is provided atdiametrically opposite sides with slots 26 for receiving the fusibleelement in a manner to be described later. The center of the disk ispunched upwardly to form an offset portion 2'I which carries indicia 28Corresponding to the rating of the fuse. As shown by Fig. 3, when inassembled position the offset portion 21 forms a space or chamber 28 forreceiving the peened-over end 22 of the center contact I3 so that thedisk I8 will lie flat against the plate I9 when held in assembledposition by the screw shell.

In assembled position one end of the fusible element or link II extendsthrough one of the recesses 26 in the disk I8 and the end is then bentbackwardly into a recess 29 formed in the outer wall of the insulatingbody and secured in any suitable manner, such as by solder 30, to theupper edge of the screw-threaded member I2. Within the recess I5 thefuse link extends upwardly in a loop to a point adjacent the window I6and the looped portion of the link is provided with indicia 3lcorresponding to the rating of the fuse at a point adjacent the windowI6. The indicia are readily visible through the window and are enlargedby the lens effect resulting from the use of the curved surface I'I. Theopposite end of the fuse link extends through the other of the recesses26 in the disk I8 and then passes into the chamber 28 where it i ssecured to the center contact I3 in any suitable manner such as bysolder 32.

The indicia 28 are readily visible through the Window I6 at one end ofthe fuse body, even though they are positioned at the opposite end ofthe body on the disk I8 which forms a portion of the closure for therecess I5. This means that it is unnecessary to position additionalindicating means, such as a piece of indicia bearing paper within therecess I to indicate the rating of the fuse. Since the entire insulatingbody of the fuse is formed of transparent material, a very large lightgathering area is attained so that the interior of the plug fuse isclearly visible for easy reading of the indicia 28. The disk lil and theplate I9 form an exceptionally strong closure for the recess I5 and arewell able to withstand the pressures incident to volatilization of thefuse link upon short circuit. Since the disk and plate are formed ofrelatively llow cost material, such as sheet fiber, it will be apparentthat the overall cost of the fuse is considerably reduced withoutsacrificing strength or interrupting capacity of the fuse. The offsetportion 21 of the disk I8 forms in effect an arch which greatlystrengthens the disk and prevents it from being ruptured or blown outupon short circuit. Venting of the interior of the fuse body will beeffected through the -recesses 126 'in the disk I3 'and the spacesformed by the clearances between the screw shell and the threads 23 ofthe fuse body. Some of the -gases will also pass through the passage 29.Upon short circuit, the resulting arc cannot travel along the fuse linkto the center contact I3 inasmuch as it will be snu'ifed out vat thepoint where the link passes through the 4left-hand groove -25 in thedisk I8 before it can enter 'the chamber 28.

While I prefer to make vthe insulating 'body of the lfuse ofYtransparent material in order to render the rating indicia of the diskI3 clearly visible, it should be manifest that in some cases the body ofthe 'fuse may be made of opaque .insulating material with a separatetransparent window-at the top Vfor viewing of the indicia.

What I claim as new and desire -to secure by Letters Patentof AtheUnitedStates is:

1. vA plug fuse comprising a'body of insulating material having a recessextendingfrom one end thereof, a fusible elementdisposedlin'said'recess, a disk of insulating material resting on theendWall of said body closing said recess, said disk having a central archedportion extending slightly into said recess, a plate of insulatingmaterial adjacent said insulating disk and having a center contactmounted therein and a threaded screw shell mounted on said base andhaving a flange engaging said insulating plate to secure said disk andplate in position on said base, one end of said fusible element beingelectrically connected to said screw shell and the other end beingconnected to said center contact.

2. Aplug fuse comprising a body of insulating material having a recessextending from one end thereof, a fusible element disposed in saidrecess, a disk of Vinsulating material having an offset center portiondisposed at the said one end of the body to close said recess, a plateof insulating material adjacent said insulating disk and having a centercontact mounted therein, and a threaded screw shell mounted on said baseand having a flange engaging said insulating plate fto secure said plateand disk in position on said base, one end of said fusible element beingelectrically connected to said screw shell and the other end beingconnected to the center contact in the space between the disk and plateformed by the offset portion of said disk.

3. A plug fuse comprising a body of insulating material having a recessextending from one end thereof, a fusible element disposed in saidrecess, a disk of insulating material having an offset portion, saiddisk vbeing disposed at the said one end of the body closing saidrecess, said disk being provided with opposite slots, a plate ofinsulating material adjacent said insulating disk and having a centerContact -mounted thereon, and a threaded screw shell mounted on saidbase and having a `flange engaging said insulating plate to secure saidplate and disk in position on said base, one end of said fusible elementextending through one of the slots in said insulating disk and beingelectrically connected to `said screw shell, the other end of saidfusible element extending through the other .of said .slots and beingconnected to said .center contact in the space between said plateanddisk formed by the offset portion of said disk.

FRED' G. voN HOORN.

